26
4.2
System Reset
CW6632B Bluetooth 3.0 Audio Player SOC
Version 1.0.0
Copyright ©2015, www.appotech.com. All Rights Reserved.
Watchdog reset
POR reset
LVD reset
System Reset
OR
Port wakeup reset
RTCC reset
Figure 4-2 Reset Sources
4.2.1
LVD
CW6632B provides 4 levels programmable Low Voltage Detector (LVD) for user to detect VDDLDO power supply
voltage or external pin voltage multiplexed with GPIO P3.3. It is for doing so since VDDLDO is the input voltage
source for on-chip Low-Drop-Out regulator (LDO) and that supplies power to internal VDDCORE. User for such
reason can momentarily monitor the VDDLDO power if externally connects to some batteries and detect if external
power source starts dropping to a level that CW6632B LDO cannot tolerate and can do proper actions in the system
program.
LVD can also be used to monitor external voltage source through the GPIO P3.3 to enhance programmability for
different voltage levels. One of the examples can be used to monitor external power sources or batteries voltage or
some voltages related to say pressure or temperature. It is there to provide a simple interface compared to ADC
since ADC requires more programming space and procedures to detect precise voltage level. If user requires
un-precise voltage detection without fine voltage range, LVD will be a good choice compared to ADC
measurement.
illustrates different voltage detection levels.
Remark:
When LVD_ENB is enabled, there is approximately 100us for the band-gap and the comparator to be stable
before the end-user can use it as low voltage detection. During the time, LVD_OEB has to be H in order to
disable the LVD output with possibly fluctuating signal level.
Different power supply falling time will affect the voltage detection. It is recommended that the power supply
falling time should be larger than 1ms for stable low voltage detection.
Upon detection occurs, interrupt can be generated if LVD interrupt is enabled, or, CW6632B can undergo reset if
interrupt is disabled.
Note that the detection is slightly dependent on power supply falling rate and noise fluctuation during power drop
may alter the detection results. For this reason, internally the comparator has about 150mV hysteresis voltage level
defined as VHYS = VLVDR-VLVDS to filter out the noise may occur. Also, the detection level may have a maximum
of 100mV difference compared to the value stated in
Table 4-1 LVD level setting
BORS[3:0]
Detected VDDLDO V
BORS[3:0]
Detected VDDLDO V
4'b0000
2.200
4'b1000
3.267
